Biosensors typically are devices that allow qualitatively or quantitatively detection of target molecules, also called “analytes”, such as e.g. proteins, viruses, bacteria, cell components, cell membranes, spores, DNA, RNA, etc. in a liquid, such as for example blood, serum, plasma, saliva, tissue extract, interstitial fluid, cell-culture extract, food or feed extract, drinking water, . . . . In almost all cases, a biosensor uses a surface that comprises specific recognition elements for capturing the analyte. Therefore, the surface of the sensor device may be modified by attaching specific molecules to it, which are suitable to bind the target molecules which are present in the liquid.
One of the measuring principles is the counting of labelled molecules attached at predetermined sites on the biosensor. For example, the molecules may be labelled with magnetic particles or beads and these magnetic particles or beads can be detected with a magnetic sensor. Alternatively, the amount of analyte may be detected by fluorescence. In this case the analyte itself may carry a fluorescent label, or alternatively an additional incubation with a fluorescent labelled second recognition element may be performed.
In most biosensors, a sensor chip is provided with a dry reagent and a detector surface covered with a biologically-active surface coating. The reagent may e.g. comprise labels coupled to biologically-active moieties, e.g. an anti-drug antibody. When the test fluid arrives, the dry reagent dissolves and mixes into the fluid. Thereafter the fluid is transported towards the sensor surface and wets the sensor surface. The labels as well as the sensor are exposed to the drug molecules. This influences the binding of the labels to the sensor surface, which is detected.
Electrochemical biosensors are known, e.g. from US 20050016844 A1, in the form of test strips wherein a dry dissolvable layer is provided near or on the electrodes. The layer generally comprises chemical components for reacting with the analyte or target molecule to produce an electrochemical signal that represents the presence of the analyte in the sample fluid, such as one or more enzymes, co-enzymes, co-factors, buffer salts, and adjuvants to enhance the reagent properties or characteristics such as de- and rehydration. The latter typically is used for detecting analytes present in relatively high concentrations in the sample.